News update: COVID-19

28 June 2021 Newsletter

Fortunately, the tide seems to be turning in the Netherlands with regard to SARS-CoV-2! A positive difference, when we compare the situation now with previous COVID-19 waves is the sharp rise in the number of people who have been fully or partially vaccinated.

This newsletter provides you with a brief update on the following topics:

  1. Antigen rapid tests: is there any news?
  2. Practical issues related to vaccination
  3. COVID-19 antibodies/serology
  4. Health checks: additional service

I. Antigen rapid tests: is there any news?
The main point is that an antigen rapid test is less accurate than a polymerase chain reaction (PCR) test. The sensitivity of a rapid test is generally sufficient when someone is presenting with symptoms. If a rapid test returns a false negative (i.e. the result was negative, but a PCR test later confirms the person does have COVID-19) then that person was in all probability not (very) contagious for his/her contacts on the day of the previously negative rapid test. That is often sufficient for a normal (work) situation, other than those where a person cannot or does not want to allow him/herself to be affected.

A self-test uses the same principle as an antigen rapid test. However, the idea behind these self- tests is that they are intended to promote early detection of COVID-19 in persons who have symptoms. In other words, these tests are not intended for people with symptoms. And not for if a person has had contact with a COVID-19 patient or if they have returned from an orange area/country! Our main concern is that self-testing is being used for purposes other than those for which it was designed. The sensitivity of self-tests is known, in fact, to be much lower than the professionally applied antigen rapid tests, sometimes barely above 50-60%.

Unfortunately, to undergo an antigen rapid test is not necessarily a pleasant experience, but there is some potentially good news in this area. Saliva pen tests have been developed and are presently being refined, in which a test subject sucks on a sponge for 2 minutes. After 15-30 minutes incubation of the saliva sample, a test result can be read with reasonable reliability. We are following this development closely and are already using this technique in some situations. It goes without saying that the reliability is higher in those with symptoms. If you are interested, please contact us for further information.

II. Practical issues related to vaccination

A. COVID-19 versus non-COVID vaccination
The official line remains: do not administer a COVID-19 vaccination at the same time as a non- COVID vaccination, for example a vaccination which is required for travel. In fact, this is somewhat old-fashioned advice that dates back to a time when there was less experience of COVID-19 vaccinations. By separating vaccinations in terms of timing, it is easier to attribute side effects to vaccine A or B than when several vaccines are administered simultaneously. For logistical reasons, it can sometimes be particularly inconvenient to schedule multiple vaccinations, especially since a complete vaccination involving one or more vaccines depending upon which vaccine is administered requires multiple administration times anyway. In such cases, simultaneous administration of COVID-19 and any non-COVID vaccines is not a problem. However, this depends on the willingness of the organisation that vaccinates people to perform such simultaneous vaccinations.

B. Timing/interval period of COVID-19 vaccinations
Regarding the timing of COVID-19 vaccinations, when one is vaccinated with a vaccine consisting of two separate doses, does it matter how far apart these are administered? The general advice is: stick to the recommended interval between the two doses whenever possible. If this is not possible for practical reasons, the rule is: you can stretch the interval, but you cannot shorten it. Doing the latter will most likely decrease the effectiveness of the vaccination.

C. Complete the COVID-19 vaccination process with another type of vaccine: possible or not?
Another question is whether the vaccination process may be completed with a different vaccine than the one with which it was started. The short answer is that, for the time being, the advice is to complete the process with the same vaccine as the one that was given initially. If this is not possible (for example, if a vaccine that is not available in the Netherlands was given abroad), the following applies: if the vaccine has been approved by the European Medicines Agency (EMA), the vaccination process may be completed with a vaccine from the same class as a vaccine that is available in the Netherlands. If it concerns a non-EMA-approved vaccine, then the advice is to restart a full vaccination process with a vaccine that is available in the Netherlands.

If a person has experienced severe side effects from a particular type of vaccine, for example an mRNA vaccine, and there is a contraindication for administering the second vaccination, then after an interval of at least 4 weeks the person may complete the process with a vector vaccine. It may be that more side effects occur in such a case, but this is not necessarily. Research is still being done into the ultimate protection that is built up in such a case. In theory, it could be less, the same or even greater.

D. SARS-CoV-2infection and vaccination: still needed and if so, how much?
For a person with an otherwise intact immune system who has experienced COVID-19, only one booster vaccination is sufficient. This is true even if the vaccine with which they are vaccinated normally requires two doses.

E. Yellow booklet and/or Corona Check App
An important practical point: make a note of your vaccination in your yellow vaccination booklet (yellow booklet available from us on request), where possible, and make sure that your vaccination certificate is linked to the Corona Check App that will be available from now on. Traveling with a paper certificate is certainly possible for the time being, but a digital proof is sometimes also useful! As a side note: we are working on linking our test results to the Corona Check App as well, but at present such a connection is not being made very easy by the managing authorities …

F. Testing after vaccination: necessary or not? And which test?
Vaccination should result in the body making antibodies against the SARS-CoV-2 virus. Generally speaking, this protection is high, although there are (and with a view to the future will be) virus variants against which the protection is somewhat lower. These antibodies can be measured in the blood (serology).

However, protection after vaccination is unfortunately not 100%. This means that in case of symptoms, testing will still be necessary for the time being. Of course, it is hoped that the urgency of testing in case of symptoms after vaccination will slowly diminish as infection rates decline worldwide and especially when it becomes apparent that the vast majority of the world’s population (excluding people with severely impaired immune systems) is sufficiently protected after vaccination against serious illness or death in the unlikely event of contracting COVID-19. Even after vaccination, a PCR or an antigen rapid test can still be used to demonstrate SARS- CoV-2 infection. The result is therefore not influenced by a person’s vaccination status.

It is also advisable to check carefully, before travelling abroad, whether the destination country has already accepted a complete series of vaccinations as an entry requirement. In Europe and an increasing number of non-European countries, this is increasingly the case, but not always! It is therefore possible that the country you are travelling to requires an additional negative result from a quick test or PCR, despite proof of a complete vaccination series. Something to bear in mind in planning one’s journeys!

III. COVID-19 antibodies/ serology

Unfortunately, if you are asked to provide proof of COVID-19 antibody status for any reason you may not always have proof of a previous infection. You may also have a personal interest in knowing whether you have experienced COVID-19 in the past or you may want to know whether vaccination has actually led to the production of antibodies (non-mandatory). You can come to us for the blood test required for this. From a technical point of view, it is theoretically possible to distinguish antibodies produced after vaccination from antibodies produced after a natural infection. However, in practice, this is rarely important, and the most common serological tests are not able to do so. The important question is, therefore: are antibodies present or not?

IV. Health checks: additional service

Finally, we have noticed that slowly but surely more people are travelling again and that the demand for periodic health checks has clearly increased recently. We have made an agreement with a number of companies to call up employees who are eligible for these checks ourselves in order to relieve them of this administrative chore. This is done via our secure portal so that privacy is fully guaranteed. If you also want to use this free service, please let us know. We would also like to draw your attention to the possibility of expanding the health check either as a one off or periodically, with a lung function test. This is in response to questions from employees who would like to have more clarity on this point in connection with a COVID-19 infection.

If you have any additional questions, please contact us at We can also be reached by telephone during opening hours or via our website

At weekends we are open for COVID-19 testing by appointment from 09:00-11:00.

Kind regards on behalf of our Management Team,

Dr Lennert Slobbe, internist-infectiologist



Leave a Reply

Your email address will not be published. Required fields are marked *