SINGAPORE - Covid-19's death toll here stands at 44, with seven recent deaths in August. All of these fatalities were among unvaccinated people, five of whom had multiple pre-existing conditions such as diabetes, heart disease and cancer.

As these diseases are highly prevalent among the local population, The Straits Times looks at why they make people more susceptible to severe Covid-19 infection, and why it is important to get them vaccinated.

Q: Many of those who died from Covid-19 had diabetes, or cardiac conditions such as hypertension, high cholesterol and heart disease. Why are people with these conditions more at risk of severe disease if they were to get Covid-19?

A: Professor Tan Huay Cheem, a senior consultant at the Department of Cardiology at the National University Heart Centre, Singapore, said that most of these patients tend to be elderly people who are severely ill with frequent and chronic comorbidities (having more than one chronic condition).

However, he noted that any cardiac condition, such as coronary artery disease or heart failure, seems to be a major risk factor for an "unfavourable outcome" from Covid-19 infection.

Covid-19 patients with underlying heart conditions are six times more likely to be hospitalised than those without any pre-existing conditions, he said. Their mortality rate is also 10 times higher.

Similarly, the Covid-19 mortality rate is seven times higher for diabetic patients, and six times higher for those with hypertension (high blood pressure).

While it is not yet clear how these risk factors make a patient more susceptible to Covid-19 infection, Prof Tan said that hypertension and diabetes mellitus are associated with an underlying chronic inflammatory state.

If they get Covid-19, they are more likely to experience even more inflammation in the body, which is linked to many Covid-19 complications.

Dr Bee Yong Mong, vice-president of charity organisation Diabetes Singapore, said diabetics are more prone to severe illness such as pneumonia due to many factors, one of which is having defects in their immune defence mechanism.

He added that those who do not have well-controlled diabetes often have high blood glucose levels, which could inhibit white blood cell functions that are important in overcoming Covid-19 infection.

Q: Why are cancer patients more at risk of developing severe disease, and can all cancer patients get vaccinated?

A: Associate Professor Iain Tan, a senior consultant at the Division of Medical Oncology from the National Cancer Centre Singapore (NCCS), said that the large majority of cancer patients can receive mRNA Covid-19 vaccinations.

"For patients currently on active cancer treatment like chemotherapy, radiation therapy or immunotherapy, their primary oncologists should review their cancer status and ongoing cancer treatment to assess their eligibility for vaccination."

He added that their oncologists should also advise the optimal timing of the vaccinations in relation to the cancer treatment.

The Ministry of Health had on July 28 relaxed the criteria for severely immunocompromised people to be vaccinated. This included those undergoing cancer treatment or who have received a transplant within the past three months.

However, certain groups of patients who may not be currently suitable for vaccination include patients undergoing very highly immunosuppressive chemotherapy, said Prof Tan.

Immunosuppressive treatments lower the activity of the body's immune system.

Professor Goh Boon Cher, a senior consultant at the Department of Haematology-Oncology at National University Cancer Institute, Singapore, said: "Patients with cancer who are receiving immunosuppressive therapy like chemotherapy or bone marrow transplant have weakened immune systems that cannot mount an adequate response to viral infection."

In addition, Prof Tan from NCCS said that studies have shown that vaccinated cancer patients who are receiving chemotherapy may produce a reduced antibody response after their first dose, however, an adequate antibody response is generally achieved after their second dose.

"Therefore, it is important for cancer patients to complete both doses of vaccination to reduce the risk and severity of a Covid-19 infection," he added.

Dr Chng Shih Kiat, medical director and consultant family physician at Raffles Medical, said that patients with conditions such as hypertension, diabetes and heart disease are not considered immunocompromised.

Q: Will the vaccine still work on me if I have these chronic conditions?

A: Yes. However, if you are immunocompromised, the effectiveness of the vaccine may be reduced.

Therefore, the Expert Committee on Covid-19 Vaccination has said that it is important to continue taking precautions to prevent infection, such as by avoiding crowded places and practising good hand hygiene.

Household members of immunocompromised people are also urged to get vaccinated to reduce the risk of being infected and transmitting the virus to them.

Dr Chng said that people with chronic conditions can take mRNA vaccines.

They will only be recommended to go for the Sinovac vaccine if they meet the following criteria:

• Had a possible allergic reaction or anaphylaxis to a first dose of mRNA vaccine
• Had prior episodes of allergy or anaphylaxis to other vaccines
• Had a recent transplant within the last three months
• Are on aggressive immunotherapy or are in an immunocompromised state from HIV infection

Associate Professor Piotr Chlebicki, a senior consultant at the Department of Infectious Diseases at Singapore General Hospital, said that it is all the more important for people with chronic conditions to get vaccinated, as they are more likely to develop severe disease compared with healthy individuals.

He added that the hospital has a mobile vaccination team to help those who are immunocompromised and warded there to get their jabs.

7 deaths so far this month - all unvaccinated

• Aug 1: A Ukrainian man, 34, who was a sea crew member who arrived in Singapore on board a vessel. It is not known whether he had any underlying medical conditions.
• Aug 2: Singaporean woman, 58, who was a household contact of a case who had visited Samy's Curry restaurant, which has more than 60 cases linked to it. She had no underlying conditions.
• Aug 4: Singaporean man, 79, who had a history of heart disease, chronic obstructive pulmonary disease and hypertension (high blood pressure).
• Aug 5: Singaporean man, 63, who had a history of heart disease, stroke, diabetes, hypertension and hyperlipidaemia (high cholesterol).
• Aug 7: Singaporean woman, 80, who had a history of diabetes, hypertension and atrial fibrillation, a heart condition that causes an irregular and often abnormally fast heart rate.
• Aug 11: Singaporean man, 69, who had a history of stroke, diabetes, hypertension and hyperlipidaemia.
• Aug 13: Singaporean man, 84, who had a history of cancer, heart disease, diabetes, hypertension and hyperlipidaemia.