Why Pfizer still recommends the second dose of Covid vaccine at 21 days

For the CTS, the recall of Pfizer a vaccines can be postponed up to 42 days, but the company continues to recommend compliance with the indicated deadlines

(photo: Unsplash) On 5 May the Technical Scientific Committee ( Cts) expressed the opinion that it is possible to postpone the second dose of Pfizer and Moderna vaccine until 42 days after the first administration (instead of 21 and 28 days later, respectively). A timing change that would certainly allow vaccine protection to be extended to more people over the same period, and which has already been practiced in countries like the UK. However, companies cannot endorse the initiative and continue to recommend compliance with the ways and times by which vaccines were approved for emergency use by the European Medicines Agency (EMA). Why?

The reasons of the companies

The anti-Covid vaccines have been approved by the EMA for emergency use based on the evidence of clinical trials conducted by the manufacturers. These trials have so far verified the efficacy of vaccines according to methods and times defined a priori: two administrations at a distance of 21 days for Pfizer and two administrations at a distance of 28 days for Moderna. There are no official data that have monitored the efficacy of vaccines with protocols at more dilated intervals.

"The vaccine was designed for a second administration at 21 days. At the moment we have no data on a longer range of administration except in real life observations, as has been done in the United Kingdom ”, Valeria Marino, medical director of Pfizer Italia reiterated on Sky Tg24. “It is an evaluation by the CTS, we will observe what happens. Like Pfizer, however, I say to stick to what has emerged from the scientific studies because this guarantees the results that allowed the authorization ".

The reasons for the Cts

The recommendation of the Cts is more than anything else a compromise between the scientific evidence and the real life data of the countries that have decided to extend the interval between first and second dose put in relation to the numbers of the coronavirus in Italy and the availability of vaccines.

If it is true that there are no published studies that have assessed the effectiveness of mRna vaccines by postponing the administration of the second dose, it is also true that after two weeks from the first the protection conferred is already very good on average and it is considered unlikely that it will degrade quickly. And then there are the positive experiences abroad, in fact.

The opinions of the experts

Several Italian experts (from Silvio Garattini of the Mario Negri Institute of Pharmacological Research to Matteo Bassetti of the Clinic of Infectious Diseases of the San Martino hospital in Genoa, in Fabrizio Pregliasco of the University of Milan) consider the indications of the CTS to be common sense, to extend the protection (partial, but still more than acceptable) to as many people as possible in less time.

While recognizing the needs dictated by the contingent situation, there are also those who underline that certainties are very few and that in ideal conditions the choice to keep the call to 21 days or to postpone it should be evaluated on the person : we are not all the same and we respond differently to vaccines, especially if we are older in age or if there are immune problems.

Others raise potential communication and trust problems of the p vaccine regulation: changing methods and times could generate confusion and could increase the number of people who, perhaps a little uncertain from the start, give up the booster.


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