The agency says that so far, only studies on coronavirus vaccinations where precisely 21 days elapse between the first and second injection are reliable. In the U.K., the period between doses obtained from Pfizer, the same firm which has supplied Estonia's vaccinations to date, has been extended to 12 weeks, with second doses potentially not even taking place, something the Estonian medicines agency does not recommend.

Only studies performed so far with exactly 21 days between injections can be relied upon, the agency says.

Half of the Pfizer/BioNTech vaccinations arriving in Estonia will be immediately used, with the rest kept in reserve for 21 days until the second dose is administered.

Medicines agency deputy director: Two doses the recommended level

The medicines agency says that while the U.K.'s Joint Vaccination and Immunization Committee takes the view that keeping a second dose in reserve is not needed, since the first injection provides adequate protection and therefore it makes more sense to inject a second individual instead, Katrin Kiisk, deputy director at the State Agency of Medicines, says conversations about the effectiveness of one dose are irrelevant since research has so far revealed that two doses are recommended.

Kiisk said "One early phase study of the vaccine did evaluate the effects of a single dose. Subjects received 60 mg, which is twice the dose of the authorized vaccine. The amount of virus neutralizing antibodies was then measured, which was consistently low, which in turn demonstrates that a second dose is required to provide an effective protective response in the body."

Kiisk said that two doses were needed to ensure 95 percent effectiveness of the vaccine, from around seven days after the second dose.

A more comprehensive study saw over 20,000 individuals receive the initial 60 mg, divided into two, i.e. 30 mg each, administered 21 days apart.

UK authorities differ

Pfizer itself says the first dose provides around 50 percent temporary protection; British immunologists have cited an up-to-90-percent protection rate, ERR reports.

The U.K. system, with up to 84 days between vaccinations, was imposed from December 31.

Katrin Kiisk also said that the point of vaccine trials is not to ascertain how a first dose works, which can be deduced from study results, though this is a matter of opinion more than fact and that further testing is needed.

Over time, we will certainly get more information, but for now we have that information based on research. The rest is all a bit hypothetical and we can still recommend to follow the current drug information," she said.

All that could be largely certain is that two injections are better than one, Kiisk said, even if extending or shortening lead times between first and second vaccines may not make a difference.

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